scholarly journals The Protective Role of Bark and Bark Fibers of the Giant Sequoia (Sequoiadendron giganteum) during High-Energy Impacts

2020 ◽  
Vol 21 (9) ◽  
pp. 3355
Author(s):  
Georg Bold ◽  
Max Langer ◽  
Laura Börnert ◽  
Thomas Speck
Keyword(s):  
Energy Dissipation ◽  
Sierra Nevada ◽  
High Energy ◽  
Protective Role ◽  
Compression Tests ◽  
Dynamic Impact ◽  
Thin Sections ◽  
Single Fibers ◽  
Giant Sequoia ◽  
Sequoiadendron Giganteum

The influences of (1) a high fiber content, (2) the arrangement of fibers in fiber groups, and (3) a layered hierarchical composition of the bark of the giant sequoia (Sequoiadendron giganteum) on its energy dissipation capability are analyzed and discussed regarding the relevance for an application in bioinspired components in civil engineering. The giant sequoia is native to the Sierra Nevada (USA), a region with regular rockfalls. It is thus regularly exposed to high-energy impacts, with its bark playing a major protective role, as can be seen in the wild and has been proven in laboratory experiments. The authors quantify the fundamental biomechanical properties of the bark at various length scales, taking into account its hierarchical setup ranging from the integral level (whole bark) down to single bark fibers. Microtensile tests on single fibers and fiber pairs give insights into the properties of single fibers as well as the benefits of the strong longitudinal interconnection between single fibers arranged in pairs. Going beyond the level of single fibers or fiber pairs, towards the integral level, quasistatic compression tests and dynamic impact tests are performed on samples comprising the whole bark (inner and outer bark). These tests elucidate the deformation behavior under quasistatic compression and dynamic impact relevant for the high energy dissipation and impact-damping behavior of the bark. The remarkable energy dissipation capability of the bark at the abovementioned hierarchical levels are linked to the layered and fibrous structure of the bark structurally analyzed by thin sections and SEM and µCT scans.

Dislocations in alumina deformed by prismatic slip

1978 ◽  
Vol 36 (1) ◽  
pp. 606-607
Author(s):  
J. Cadoz ◽  
J. Castaing ◽  
J. Philibert
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Basal Slip ◽  
Prismatic Slip ◽  
Compression Tests ◽  
Thin Sections ◽  
Burgers Vector ◽  
Maximum Deformation ◽  
Transmission Electron ◽  
Mechanical Thinning

Plastic deformation of alumina has been much studied; basal slip occurs and dislocation structures have been investigated by transmission electron microscopy (T.E.M.) (1). Non basal slip has been observed (2); the prismatic glide system <1010> {1210} has been obtained by compression tests between 1400°C and 1800°C (3). Dislocations with <0110> burgers vector were identified using a 100 kV microscope(4).We describe the dislocation structures after prismatic slip, using high voltage T.E.M. which gives much information.Compression tests were performed at constant strainrate (∿10-4s-1); the maximum deformation reached was 0.03. Thin sections were cut from specimens deformed at 1450°C, either parallel to the glide plane or perpendicular to the glide direction. After mechanical thinning, foils were produced by ion bombardment. Details on experimental techniques can be obtained through reference (3).

Late Pleistocene Vegetation of Kings Canyon, Sierra Nevada, California

1983 ◽  
Vol 19 (1) ◽  
pp. 117-129 ◽  
Author(s):  
Kenneth Cole
Keyword(s):  
Plant Community ◽  
Sierra Nevada ◽  
Late Pleistocene ◽  
Coniferous Forest ◽  
Pollen Grains ◽  
Mean Annual Precipitation ◽  
Juniperus Occidentalis ◽  
Sequoiadendron Giganteum ◽  
Western Side ◽  
Modern Sample

AbstractSeven packrat midden samples make possible a comparison between the modern and late Pleistocene vegetation in Kings Canyon on the western side of the southern Sierra Nevada. One modern sample contains macrofossils and pollen derived from the present-day oak-chaparral vegetation. Macrofossils from the six late Pleistocene samples record a mixed coniferous forest dominated by the xerophytic conifers Juniperus occidentalis, Pinus cf. ponderosa, and P. monophylla. The pollen spectra of these Pleistocene middens are dominated by Pinus sp., Taxodiaceae-Cupressaceae-Taxaceae (TCT), and Artemisia sp. Mesophytic conifers are represented by low macrofossil concentrations. Sequoiadendron giganteum is represented by a few pollen grains in the full glacial. Edaphic control and snow dispersal are the most likely causes of these mixed assemblages.The dominant macrofossils record a more xeric plant community than those that now occur on similar substrates at higher elevations or latitudes in the Sierra Nevada. These assemblages suggest that late Wisconsin climates were cold with mean annual precipitation not necessarily greater than modern values. This conclusion supports a model of low summer ablation allowing for the persistence of the glaciers at higher elevations during the late Wisconsin. The records in these middens also suggest that S. giganteum grew at lower elevations along the western side of the range and that P. monophylla was more widely distributed in cismontane California during the Pleistocene.

scholarly journals Analysis of rock mass dynamic impact influence on the operation of a powered roof support control system

2018 ◽  
Vol 29 ◽  
pp. 00006 ◽  
Author(s):  
Dawid Szurgacz ◽  
Jaroław Brodny
Keyword(s):  
Rock Mass ◽  
Real Life ◽  
High Energy ◽  
Hard Coal ◽  
Underground Excavation ◽  
Dynamic Impact ◽  
Support Unit ◽  
Geological Conditions ◽  
Innovative Solutions ◽  
Roof Support

A powered roof support is a machine responsible for protection of an underground excavation against deformation generated by rock mass. In the case of dynamic impact of rock mass, the proper level of protection is hard to achieve. Therefore, the units of the roof support and its components are subject to detailed tests aimed at acquiring greater reliability, efficiency and efficacy. In the course of such test, however, it is not always possible to foresee values of load that may occur in actual conditions. The article presents a case of a dynamic load impacting the powered roof support during a high-energy tremor in an underground hard coal mine. The authors discuss the method for selecting powered roof support units proper for specific forecasted load conditions. The method takes into account the construction of the support and mining and geological conditions of an excavation. Moreover, the paper includes tests carried out on hydraulic legs and yield valves which were responsible for additional yielding of the support. Real loads impacting the support unit during tremors are analysed. The results indicated that the real registered values of the load were significantly greater than the forecasted values. The analysis results of roof support operation during dynamic impact generated by the rock mass (real life conditions) prompted the authors to develop a set of recommendations for manufacturers and users of powered roof supports. These include, inter alia, the need for innovative solutions for testing hydraulic section systems.

Trans-California seismic profile, death Valley to Monterey Bay

1973 ◽  
Vol 63 (2) ◽  
pp. 571-586
Author(s):  
Dean S. Carder
Keyword(s):  
Sierra Nevada ◽  
Upper Mantle ◽  
Central Valley ◽  
Test Site ◽  
Seismic Profile ◽  
High Energy ◽  
High Yield ◽  
Western Coast ◽  
Monterey Bay ◽  
Owens Valley

abstract An experiment to investigate the major earth structure along a profile from the Nevada Test Site (NTS) to the Pacific Ocean across two sections of the Sierra Nevada, one in the Kings Canyon area and the other which includes Huntington Lake, was undertaken by the Earthquake Mechanism Laboratory of the National Oceanic and Atmospheric Administration (NOAA). Instrumental coverage included 35 temporary and seven permanent seismographs. Energy sources included four high-yield and 20 intermediate- to low-yield nuclear explosions under the NTS, one high-yield explosion under Amchitka Island of Alaska, two earthquakes near Santa Rosa, and one earthquake in Monterey Bay. An upper-mantle speed of 7.9 km/sec satisfied most of the observed data except under the Sierra where the velocity was somewhat lower than this. An earthquake in Monterey Bay helped to close the west end of the profile. The Sierra Nevada “root” in large part can be attributed to relatively low upper-mantle speed under the Sierras (estimated at 7.64 km/sec) which extends to an indefinite depth and which possibly may serve as lens to refract late arriving high-energy waves to coastal areas. Crustal thickness from the Sierra foothills eastward varies from 25 to 35 km, the thinner portion under the Sierra crest and Owens Valley, near Independence, and the thicker sections under the western Sierra and the basin ranges east of Owens Valley. West of Fresno, the crust thins more or less gradually to about 20 km in thickness under the western coast ranges. This profile contrasts with that from an earlier study, across the Central Valley south of Stockton, where no such thinning under the Central Valley was observed. The sub-Sierra crust east of Fresno is somewhat complicated. Low-angle thrusting toward the east is indicated.

scholarly journals Effects of coal's initial macro-cracks on rockburst tendency of rock–coal composite samples

2019 ◽  
Vol 6 (11) ◽  
pp. 181795 ◽  
Author(s):  
Shaojie Chen ◽  
Dawei Yin ◽  
Huimin Liu ◽  
Bing Chen ◽  
Ning Jiang
Keyword(s):  
Energy Dissipation ◽  
Elastic Energy ◽  
Composite System ◽  
Structural Instability ◽  
Uniaxial Loading ◽  
Test Results ◽  
Compression Tests ◽  
Loading Direction ◽  
Attenuation Index ◽  
Composite Samples

In the present study, uniaxial compression tests were conducted on sandstone–coal composite samples to investigate the effects of original macro-cracks in coal on the rockburst tendency. First, the energy dissipation theory was used to derive the elastic energy attenuation index of composite samples during uniaxial loading. Then, based on the test results obtained, the rockburst tendency of composite samples was evaluated and analysed using the uniaxial compressive strength and elastic energy attenuation index. The results show that the original macro-cracks in coal deteriorated the rockburst tendency of composite samples. The original horizontal cracks had the lowest effect on the rockburst tendency, whereas the vertical penetrating cracks through the coal centre (parallel to the loading direction) displayed the greatest effect. The mechanism by which these macro-cracks weakened the rockburst tendency involved two steps: (i) changing the physical properties and energy accumulation conditions of composite samples and (ii) increasing the energy dissipation of composite samples during uniaxial loading. These aspects are important to understand the rockburst hazards induced by the structural instability and failure of the composite system of coal seam and roof rock during deep coal mining.

Multistable Cosine-Curved Dome System for Elastic Energy Dissipation

2019 ◽  
Vol 86 (9) ◽  
Author(s):  
Mansour Alturki ◽  
Rigoberto Burgueño
Keyword(s):  
Energy Dissipation ◽  
Analytical Model ◽  
Nonlinear Behavior ◽  
Experimental Tests ◽  
High Energy ◽  
Bistable System ◽  
Dissipated Energy ◽  
Element Analysis ◽  
The Individual ◽  
Hysteretic Response

This paper presents a new energy dissipation system composed of multistable cosine-curved domes (CCD) connected in series. The system exhibits multiple consecutive snap-through and snap-back buckling behavior with a hysteretic response. The response of the CCDs is within the elastic regime and hence the system's original configuration is fully recoverable. Numerical studies and experimental tests were conducted on the geometric properties of the individual CCD units and their number in the system to examine the force–displacement and energy dissipation characteristics. Finite element analysis (FEA) was performed to simulate the response of the system to develop a multilinear analytical model for the hysteretic response that considers the nonlinear behavior of the system. The model was used to study the energy dissipation characteristics of the system. Experimental tests on 3D printed specimens were conducted to analyze the system and validate numerical results. Results show that the energy dissipation mainly depends on the number and the apex height-to-thickness ratio of the CCD units. The developed multilinear analytical model yields conservative yet accurate values for the dissipated energy of the system. The proposed system offered reliable high energy dissipation with a maximum loss factor value of 0.14 for a monostable (self-recoverable) system and higher for a bistable system.

Test Study on the Rigidity Degradation and Energy Dissipation of High-Strength Reinforced Concrete Columns with Central Reinforcement

2010 ◽  
Vol 163-167 ◽  
pp. 398-405
Author(s):  
San Sheng Dong ◽  
Zi Xue Lei ◽  
Jun Hai Zhao
Keyword(s):  
Energy Dissipation ◽  
High Strength ◽  
Concrete Columns ◽  
High Energy ◽  
Affecting Factors ◽  
Static Test ◽  
Test Study ◽  
Core Areas ◽  
Energy Dissipation Capacity ◽  
High Energy Dissipation

Based on the pseudo-static test of 6 high-strength RC columns with central reinforcement skeletons, this paper studied their hysterisis performance, degradation of strength and rigidity, and energy dissipation capacity, with the affecting factors analyzed. The result shows that the central reinforcement skeletons can compensate for the low plasticity and brittle failure susceptibility of high-strength concrete so that all the specimens have stable strength, slow rigidity degradation and high energy dissipation capacity at later stage of loading; the larger the core areas the higher the strengths and ductility of the specimens, but slightly faster the degradation of strength and energy dissipation capacity as compared with the specimens with smaller core areas; the spacing of ties, longitudinal reinforcement ratio of core area both influence the strength degradation and energy dissipation capacity of the specimens, but they have little effect on their strengths.

Stiffness, Ductility, and Energy Dissipation of RC Elements under Cyclic Shear

2005 ◽  
Vol 21 (4) ◽  
pp. 1093-1112 ◽  
Author(s):  
Thomas T. C. Hsu ◽  
Mohamad Y. Mansour
Keyword(s):  
Energy Dissipation ◽  
High Energy ◽  
Shear Stresses ◽  
Principal Stresses ◽  
Element Analysis ◽  
Rc Structures ◽  
Cyclic Shear ◽  
Steel Bar ◽  
High Energy Dissipation ◽  
Reversed Cyclic

A new Cyclic Softened Membrane Model (CSMM) was recently developed to predict the stiffness, ductility, and energy dissipation of reinforced concrete (RC) elements subjected to reversed cyclic shear. Using the nonlinear finite element analysis, we can integrate these responses of elements to predict the behavior of a whole structure, such as a low-rise shear wall, subjected to earthquake action. This study of CSMM summarizes systematically the effects of the two primary variables: the steel bar angle with respect to the direction of the applied principal stresses and the steel percentage. The results clearly show that RC structures under cyclic shear stresses could be designed to be very ductile, have large stiffness, and possess high energy-dissipation capacities (just like flexural-dominated elements), if the steel bars are properly oriented in the directions of principal stresses and if the steel percentages are kept within certain limits.

Sign in / Sign up

Export Citation Format

Share Document